In the processing of fine materials, such as various sands, brown limestone and various ores, it is usually necessary to clean and dewater such materials and sometimes it is required that they be classified as to particle size. Such treatment in the past has been carried out in apparatus such as screw washers, sand drags, cyclones or settling tanks, or in apparatus employing moveable rakes. The screw washer or rake-employing apparatus in general has employed an elongated trough, in which the screw or rakes are positioned. The well usually contains water and sand in the suspension, and the trough embodies a discharge slope. The rake is usually moveably carried, either in a continuous fashion, as on a conveyor system for movement through the well and up the discharge slope, or in instances in which the rake has not been continuous, its movement has been actuated by mechanical mechanisms that lift the rake in a motion whereby it remains substantially parallel to the discharge slope, but moves into and out of submersion in the sand-water suspension.
Such motions of rakes are very often unsatisfactory, particularly when the sand is fine in particle size and approaches a suspension in the water, in that such systems often create turbulence which is sufficiently severe to interfere with optimum performance of the apparatus. Also in the prior art, various baffle arrangements have been suggested, that have not been entirely satisfactory.